[Intel-gfx] [PATCHv6] drm/i915/dp: change aux_ctl reg read to polling read

[Murthy, Arun R]

> -----Original Message-----
> From: Nikula, Jani <jani.nikula at intel.com>
> Sent: Thursday, December 15, 2022 4:00 PM
> To: Murthy, Arun R <arun.r.murthy at intel.com>; intel-
> gfx at lists.freedesktop.org; ville.syrjala at linux.intel.com; Deak, Imre
> <imre.deak at intel.com>
> Cc: Murthy, Arun R <arun.r.murthy at intel.com>
> Subject: Re: [PATCHv6] drm/i915/dp: change aux_ctl reg read to polling read
> 
> On Thu, 15 Dec 2022, Arun R Murthy <arun.r.murthy at intel.com> wrote:
> > The busy timeout logic checks for the AUX BUSY, then waits for the
> > timeout period and then after timeout reads the register for BUSY or
> > Success.
> > Instead replace interrupt with polling so as to read the AUX CTL
> > register often before the timeout period. Looks like there might be
> > some issue with interrupt-on-read. Hence changing the logic to polling
> read.
> >
> > v2: replace interrupt with polling read
> > v3: use usleep_rang instead of msleep, updated commit msg
> > v4: use intel_wait_for_regiter internal function
> > v5: use __intel_de_wait_for_register with 500us slow and 10ms fast
> > timeout
> > v6: check return value of __intel_de_wait_for_register
> >
> > Signed-off-by: Arun R Murthy <arun.r.murthy at intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_dp_aux.c | 15 +++++----------
> >  1 file changed, 5 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux.c
> > b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> > index 91c93c93e5fc..dec88f41380e 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp_aux.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> > @@ -40,21 +40,16 @@ intel_dp_aux_wait_done(struct intel_dp *intel_dp)
> >  	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> >  	i915_reg_t ch_ctl = intel_dp->aux_ch_ctl_reg(intel_dp);
> >  	const unsigned int timeout_ms = 10;
> > -	u32 status;
> > -	bool done;
> > -
> > -#define C (((status = intel_de_read_notrace(i915, ch_ctl)) &
> DP_AUX_CH_CTL_SEND_BUSY) == 0)
> > -	done = wait_event_timeout(i915->display.gmbus.wait_queue, C,
> > -				  msecs_to_jiffies_timeout(timeout_ms));
> > +	u32 status, ret;
> >
> > -	/* just trace the final value */
> > -	trace_i915_reg_rw(false, ch_ctl, status, sizeof(status), true);
> > +	ret = __intel_de_wait_for_register(i915, ch_ctl,
> > +				     DP_AUX_CH_CTL_SEND_BUSY, 0,
> > +				     500, timeout_ms, &status);
> >
> > -	if (!done)
> > +	if (ret == -ETIMEDOUT)
> 
> What's wrong with this comparison? Although it probably does work by
> coincidence.
> 
If (ret)
	dev_err();
Will also work, but for code readability using -ETIMEDOUT(sorry missed the declaration int ret;)

Thanks and Regards,
Arun R Murthy
--------------------

> BR,
> Jani.
> 
> 
> >  		drm_err(&i915->drm,
> >  			"%s: did not complete or timeout within %ums
> (status 0x%08x)\n",
> >  			intel_dp->aux.name, timeout_ms, status); -#undef C
> >
> >  	return status;
> >  }
> 
> --
> Jani Nikula, Intel Open Source Graphics Center